U.S. patent application number 10/856535 was filed with the patent office on 2004-12-16 for method of controlling charge and discharge of secondary battery for automatic guided vehicle.
This patent application is currently assigned to Panasonic EV Energy Co., Ltd.. Invention is credited to Fujioka, Noriyuki, Morishita, Nobuyasu, Ohkawa, Kazuhiro, Ueda, Toshifumi.
Application Number | 20040251870 10/856535 |
Document ID | / |
Family ID | 33509096 |
Filed Date | 2004-12-16 |
United States Patent
Application |
20040251870 |
Kind Code |
A1 |
Ueda, Toshifumi ; et
al. |
December 16, 2004 |
Method of controlling charge and discharge of secondary battery for
automatic guided vehicle
Abstract
To provide a method of controlling charge and discharge of a
secondary battery for automatic guided vehicle that can decide the
timing of refresh charge and discharge accurately and minimize the
frequency of refresh charge and discharge. The method of
controlling charge and discharge of a secondary battery for
automatic guided vehicle comprises a first discharge step of making
the secondary battery drive an automatic guided vehicle and
discharge electricity with a predetermined amount; a voltage
measurement step of measuring a discharge end voltage of the
secondary battery at the completion of the first discharge step;
and a charge step of performing a first charge step of charging the
secondary battery incompletely at a first charging current value
when the discharge end voltage is higher than a preset minimum
voltage, and performing a second charge step of discharging the
secondary battery fully and then charging the secondary battery
fully at a second charging current value smaller than the first
charging current value when the discharge end voltage equals the
preset minimum voltage or less.
Inventors: |
Ueda, Toshifumi;
(Toyohashi-shi, JP) ; Ohkawa, Kazuhiro;
(Kosai-shi, JP) ; Morishita, Nobuyasu;
(Toyohashi-shi, JP) ; Fujioka, Noriyuki;
(Kosai-shi, JP) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Assignee: |
Panasonic EV Energy Co.,
Ltd.
Kosai-shi
JP
|
Family ID: |
33509096 |
Appl. No.: |
10/856535 |
Filed: |
May 28, 2004 |
Current U.S.
Class: |
320/104 |
Current CPC
Class: |
B60L 53/11 20190201;
Y02T 90/12 20130101; H02J 7/0071 20200101; Y02T 10/70 20130101;
Y02T 90/14 20130101; Y02T 10/7072 20130101; B60L 53/00
20190201 |
Class at
Publication: |
320/104 |
International
Class: |
H02J 007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2003 |
JP |
2003-169679 |
Claims
1. A method of controlling charge and discharge of a secondary
battery for automatic guided vehicle comprising: a first discharge
step of making the secondary battery drive an automatic guided
vehicle and discharge electricity with a predetermined amount; a
voltage measurement step of measuring a discharge end voltage of
said secondary battery at the completion of said first discharge
step; and a charge step of performing a first charge step of
charging said secondary battery incompletely at a first charging
current value when said discharge end voltage is higher than a
preset minimum voltage, and performing a second charge step of
discharging said secondary battery fully and then charging said
secondary battery fully at a second charging current value smaller
than said first charging current value when said discharge end
voltage equals said preset minimum voltage or less.
2. A method of controlling charge and discharge of a secondary
battery for automatic guided vehicle as stated in claim 1, wherein,
in said first charge step, voltage and temperature of said
secondary battery are monitored continuously, a preset charge end
voltage is decided based on said temperature and charge is finished
when said voltage equals said preset charge end voltage or
more.
3. A method of controlling charge and discharge of a secondary
battery for automatic guided vehicle as stated in claim 2, wherein
said preset charge end voltage is decided based on said first
charging current value and said temperature.
4. A method of controlling charge and discharge of a secondary
battery for automatic guided vehicle as stated in claim 1, wherein
said second charge step is finished after a predetermined period
from start of charge.
5. A method of controlling charge and discharge of a secondary
battery for automatic guided vehicle as stated in claim 1, wherein,
in said second charge step, temperature of said secondary battery
is monitored continuously and charge is finished when a rate of
increase per unit of time in said temperature equals a
predetermined value or more.
6. A method of controlling charge and discharge of a secondary
battery for automatic guided vehicle as stated in claim 1, wherein
said secondary battery is a nickel metal hydride battery.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method of controlling
charge and discharge of a secondary battery for automatic guided
vehicle.
[0002] An automatic guided vehicle is used for automation and
laborsaving of the delivery of materials in factories and
warehouses. The automatic guided vehicle mounts a secondary battery
(battery) as a power source for a traction electric motor and a
driving source for other loads thereon and is controlled so as to
run automatically on various driving paths along a guide line such
as a guide tape adhered to the floor of factories, warehouses, etc.
When the battery needs to be charged or there is no request to
deliver materials from an operational control station, the
automatic guided vehicle moves to a charge station as a destination
and is connected to a battery charger at the charge station to
charge the secondary battery.
[0003] Conventionally, a lead storage battery has been used as the
secondary battery mounted on such automatic guided vehicle.
However, the lead storage battery takes a long time to be charged
and requires equipment for its charge and reloading as well as
personnel for maintenance. Accordingly, in these days, an alkali
storage battery such as nickel metal hydride battery, which is
capable of being quickly charged at the charge station in a short
time and requires no maintenance, has become widespread in place of
lead storage battery.
[0004] Generally, an automatic guided vehicle system placed in
factories comprises a minimum number of automatic guided vehicles
and battery chargers essential to perform desired operations so as
to reduce its total cost and prevent unnecessary space from being
occupied. After the secondary battery mounted on the automatic
guided vehicle supplies electric power to the loads for a few hours
(the automatic guided vehicle runs automatically on the driving
path), the automatic guided vehicle moves to the battery charger
automatically according to an instruction of a central control
unit. The battery charger charges the secondary battery quickly in
a few minutes. If the nickel metal hydride battery is charged fully
by quick charge, a dangerous increase in its internal pressure
causes and therefore the battery is not charged fully at quick
charge. As a result, incomplete charge and discharge of the
secondary battery is repeated. When the nickel metal hydride
battery or nickel cadmium battery is incompletely charged and
discharged repeatedly without full charge, memory effect of
increasing a voltage drop during discharge generates. In the case
where the secondary battery with the memory effect is used for
equipment in which discharge end voltage is set at a fixed value,
the apparent capacity decreases with drop in voltage. For the
secondary battery consisting of a plurality of single cells,
voltages of respective single cells differ in proportion to
accumulated discharged amount, and drop in apparent capacity and
terminal voltage of the secondary battery occurs.
[0005] The above-mentioned drop in apparent capacity and terminal
voltage can be resolved by discharging the secondary battery fully
and then performing full charge or overcharge of the secondary
battery, that is, refresh charge and discharge. A battery charge
control device for automatic guided vehicle disclosed in a patent
document 1 (Patent Publication No. 2560878) stores the number of
battery charge times and an accumulated value of charged capacity
and calculates an integrated discharged amount. When the integrated
discharged amount reaches a preset amount, the device requests the
user to perform equalizing charge.
[0006] A method of charging and discharging a secondary battery for
automatic guided vehicle of a patent document 2 (Unexamined Patent
Publication No. 2002-191103) integrates the discharged amount of
the secondary battery at the side of the automatic guided vehicle,
and when the integrated discharged amount reaches a preset amount,
requests a battery control system to perform maintenance charge and
discharge (refresh charge and discharge).
[0007] The conventional methods only measure the number of
incomplete charge (or discharge) times or total discharged amount
and determine the timing of refresh charge and discharge.
Accordingly, even if memory effect or nonuniformity of voltages of
respective single cells does not occur in fact, the methods may
request refresh charge and discharge, thereby to cause congestion
at the charge station and then interfere with the operation in
factories equipped with the automatic guided vehicle. Moreover,
there is a problem that memory effect or nonuniformity of voltages
of respectiive single cells may not be able to be detected,
resulting in sudden stop of the automatic guided vehicle.
[0008] To solve the above-mentioned conventional problems, the
present invention provides a method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
that can decide the timing of refresh charge and discharge of the
secondary battery for automatic guided vehicle accurately and
minimize the frequency of refresh charge and discharge.
BRIEF SUMMARY OF THE INVENTION
[0009] To solve the above-mentioned problems, the present invention
has the following configuration. A method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
from one aspect of the present invention has a first discharge step
of making the secondary battery drive an automatic guided vehicle
and discharge electricity with a predetermined amount; a voltage
measurement step of measuring a discharge end voltage of the
above-mentioned secondary battery at the completion of the
above-mentioned first discharge step; and a charge step of
performing a first charge step of charging the above-mentioned
secondary battery incompletely at a first charging current value
when the above-mentioned discharge end voltage is higher than a
preset minimum voltage, and performing a second charge step of
discharging the above-mentioned secondary battery fully and then
charging the above-mentioned secondary battery fully at a second
charging current value smaller than the above-mentioned first
charging current value when the above-mentioned discharge end
voltage equals the above-mentioned preset minimum voltage or
less.
[0010] The present invention has the effect of realizing the method
of controlling charge and discharge of the secondary battery for
automatic guided vehicle that can decide the timing of refresh
charge and discharge of the secondary battery for automatic guided
vehicle accurately and minimize the frequency of refresh charge and
discharge.
[0011] The secondary battery is a single cell or a battery pack
consisting of a plurality of single cells. Preferably, the single
cell is a nickel metal hydride battery or a nickel cadmium storage
battery.
[0012] Preferably, the first charge step is quick charge of the
secondary battery with a high current (the first charging current
value). The preset minimum voltage is close to a minimum voltage at
which the automatic guided vehicle using the secondary battery as a
power source is operational. In the period during which the
discharge end voltage when the secondary battery for automatic
guided vehicle supplies electricity (discharges electricity) to
loads is higher than the preset minimum voltage, the secondary
battery can be used by repeating quick charge (the first charge
step) and discharge (the first discharge step).
[0013] With the repetition of the first charge step and the first
discharge step, the discharge end voltage lowers due to memory
effect and nonuniformity of capacities of respective single cells.
When the charge start voltage is smaller than the preset minimum
voltage, the secondary voltage is discharged fully and then charged
fully at the second charging current value smaller than the first
charging current value (the second charge step). This can recover
the terminal voltage lowered by memory effect and nonuniformity of
capacities of respective single cells.
[0014] In the above-mentioned method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
from another aspect of the present invention, in the
above-mentioned first charge step, voltage and temperature of the
above-mentioned secondary battery are monitored continuously, a
preset charge end voltage is decided based on the above-mentioned
temperature and charge is finished when the above-mentioned voltage
equals the above-mentioned preset charge end voltage or more.
[0015] When the temperature of the secondary battery increases, its
internal resistance becomes smaller. The present invention can
improve control accuracy of charge by lowering the preset charge
end voltage for discontinueing quick charge as the temperature
increases (the dischargeable capacity at the completion of charge
corresponds to a target value). It can be prevented that the life
of the secondary battery is shortened due to overcharge and that a
failure in the operation of the automatic guided vehicle is caused
by insufficient charge.
[0016] In the above-mentioned method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
from another aspect of the present invention, the above-mentioned
preset charge end voltage is decided based on the above-mentioned
first charging current value and the above-mentioned
temperature.
[0017] The present invention can improve control accuracy of charge
by lowering the preset charge end voltage for discontinueing quick
charge as the temperature increases and the charging current value
decreases (the dischargeable capacity at the completion of charge
corresponds to a target value). It can be prevented that the life
of the secondary battery is shortened due to overcharge and that a
failure in the operation of the automatic guided vehicle is caused
by insufficient charge.
[0018] In the above-mentioned method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
from another aspect of the present invention, the above-mentioned
second charge step is finished after a predetermined period from
start of charge.
[0019] Preferably, the second charge step is a fixed amount
charge.
[0020] In the above-mentioned method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
from another aspect of the present invention, in the
above-mentioned second charge step, temperature of the
above-mentioned secondary battery is monitored continuously and
charge is finished when a rate of increase per unit of time in the
above-mentioned temperature becomes a predetermined value or
more.
[0021] The temperature of the secondary battery rises steeply just
before the completion of full charge. In the second charge step,
when the rate of increase in temperature becomes a predetermined
value or more, charge is finished.
[0022] In the above-mentioned method of controlling charge and
discharge of the secondary battery for automatic guided vehicle
from another aspect of the present invention, the above-mentioned
secondary battery is a nickel metal hydride battery.
[0023] The present invention is useful as, in particular, a method
of controlling charge and discharge of the nickel metal hydride
battery mounted on the automatic guided vehicle.
[0024] The novel features of the invention are set forth with
particularity in the appended claims. The invention as to both
structure and content, and other objects and features thereof will
best be understood from the detailed description when considered in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is a configuration view of a system of controlling
charge and discharge of automatic guided vehicle to which a method
of controlling charge and discharge of a secondary battery for
automatic guided vehicle in accordance with a first embodiment and
a second embodiment of the present invention is applied.
[0026] FIG. 2 is a flow chart of the method of controlling charge
and discharge of a secondary battery for automatic guided vehicle
in accordance with the first embodiment of the present
invention.
[0027] FIG. 3 is a graph showing the change in a discharge end
voltage Vend to the number of charge and discharge cycles.
[0028] FIG. 4 is a graph showing function expression of a preset
charge end voltage Vc to the battery temperature Tb of the
secondary battery 11 in the case of charge at the charging current
value I1 of 160 A, 180 A and 200 A.
[0029] FIG. 5 is a flow chart of a second charge control method in
accordance with the second embodiment of the present invention.
[0030] Part or All of the drawings are drawn schematically for
diagrammatic representation and it should be considered that they
do not necessarily reflect relative size and position of components
shown therein.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Embodiments that specifically describe best modes for
conducting the present invention will be described referring to
figures below.
[0032] <<First Embodiment>>
[0033] With reference to FIGS. 1 to 4, a method of controlling
charge and discharge of a secondary battery for automatic guided
vehicle in accordance with a first embodiment of the present
invention will be described.
[0034] FIG. 1 is a configuration view of a system of controlling
charge and discharge of automatic guided vehicle to which the
method of controlling charge and discharge of the secondary battery
for automatic guided vehicle in accordance with the first
embodiment of the present invention is applied. Reference numeral
10 denotes the automatic guided vehicle. Reference numeral 20
denotes a charge/discharge unit installed at a charge station (not
shown).
[0035] There is provided a secondary battery 11 and a battery
control part 12 for controlling the secondary battery 11 on the
automatic guided vehicle 10. Numeral 13 denotes a battery
temperature detection part and 14 denotes a voltage detection
part.
[0036] The secondary battery 11 supplies electric power to a
traction electric motor and other loads (not shown). The secondary
battery 11 is formed of a plurality of single cells as nickel metal
hydride batteries that are connected in series and in parallel with
each other.
[0037] The battery temperature detection part 13 measures anyone of
internal temperature, surface temperature and ambient temperature
of the secondary battery 11, and transmits it to the battery
control part 12. In the first embodiment, the battery temperature
detection part 13 measures a surface temperature Tb of the
secondary battery 11. Hereinafter, the surface temperature Tb of
the secondary battery 11 is referred to as a "battery temperature
Tb". The voltage detection part 14 measures voltage of the
secondary battery 11 and transmits it to the battery control part
12.
[0038] In response to a departure request or delivery request from
an operational control station (not shown), the battery control
part 12 makes the secondary battery 11 start supplying electric
power to the traction electric motor and other loads. When the
automatic guided vehicle moves to the charge station and is
connected to the charge/discharge unit 20 via a charge/discharge
line 31 and a control signal line 32, the battery control part 12
discontinues supply of electric power by the secondary battery 11
to the traction electric motor and other loads. Further, the
battery control part 12 transmits data on the battery temperature
Tb and a battery voltage V to the charge/discharge unit 20 through
the control signal line 32.
[0039] The charge/discharge unit 20 has a charge/discharge terminal
21, a control terminal 22, a source terminal 23, a rectifier filter
24, a charge/discharge part 25, a current detection part 27 and a
charge/discharge control part 28. The charge/discharge terminal 21
is connected to the charge/discharge line 31. The control terminal
22 is connected to the control signal line 32. The source terminal
23 is connected to an AC power source. The rectifier filter 24
rectifies an AC source voltage from the source terminal 23,
transforms the rectified voltage to the DC source voltage and
supplies the transformed voltage to the charge/discharge part 25.
The current detection part 27 detects a charge/discharge current
sent to the secondary battery 11.
[0040] The charge/discharge control part 28 controls the
charge/discharge part 25 based on the battery temperature Tb and
voltage received from the automatic guided vehicle 10 and the
current received from the current detection part 27. The
charge/discharge part 25 charges or discharges the secondary
battery 11 based on the control signal sent from the
charge/discharge control part 28.
[0041] The automatic guided vehicle 10 is driven by discharge of
the secondary battery 11, performs its operation, moves to the
charge station every predetermined timing according to a preset
program (for example, every one hour) and is charged quickly by the
charge/discharge unit 20 according to a first charge control method
(described later). The quick charge is set to be performed when the
state of charge of the secondary battery 11 (the ratio (%) of the
current dischargeable capacity to the dischargeable capacity at
full charge) is the order of 65%. The quick charge finishes when
the state of charge of the secondary battery 11 reaches 75%. In the
quick charge according to the first charge control method, as the
secondary battery 11 is not charged fully, increase in internal
pressure of the secondary battery 11 can be prevented. The
secondary battery 11 is used in the state of charge of 65 to
75%.
[0042] FIG. 3 is a graph showing the change in a discharge end
voltage Vend (when the automatic guided vehicle 10 is connected to
the charge/discharge unit) to the number of charge and discharge
cycles of quick charge (incomplete charge) and slight discharge. At
each cycle, the secondary battery 11 is charged with electricity
with a certain amount to go into a state of charge of 75% from a
state of charge of 65%, and discharges electricity with a certain
amount to go into a state of charge of 65% from a state of charge
of 75%. As the charge and discharge cycle is repeated, the
discharge end voltage Vend lowers and when the discharge end
voltage Vend is below a preset minimum voltage Vr (12.0 in the
first embodiment), the secondary battery 11 cannot supply
sufficient power to the loads. Memory effect is one of the factors
of lowering the discharge end voltage Vend. Since the discharged
amount from the start to the completion of discharge is
substantially constant each time (the battery discharges
electricity from a state of charge of 75% to a state of charge of
65% each time), discharge voltage drop due to memory effect is
accumulated and the discharge end voltage Vend lowers gradually.
Nonuniformity of voltages of respective single cells constituting
the secondary battery 11 also lowers the discharge end voltage
Vend. In the first embodiment, when the discharge end voltage Vend
becomes the preset minimum voltage Vr or less, the secondary
battery 11 is discharged fully and charged fully at a low current
to resolve voltage drop.
[0043] FIG. 2 is a flow chart of the method of controlling charge
and discharge of the secondary battery in accordance with the first
embodiment of the present invention. Preferably, the automatic
guided vehicle 10 is connected to the charge/discharge unit 20 each
time it discharges electricity with a substantially constant
amount. The battery control part 12 monitors voltage of the
secondary battery 11 through the voltage detection part 14 at all
times (step 201). At a step 202, the discharge end voltage Vend is
acquired. At a step 203, it is determined whether or not the
discharge end voltage Vend equals the preset minimum voltage Vr or
more. When the discharge end voltage Vend equals the preset minimum
voltage Vr or more, the operation proceeds to a step 210.
[0044] The charge/discharge control part 28 switches the
charge/discharge part 25 to a charger, controls a charging current
value I1 received from the current detection part 27 to be 200 A,
and start quick charge (step 210). At a step 211, the
charge/discharge control part 28 acquires the voltage V of the
secondary battery 11 measured by the voltage detection part 14 from
the battery control part 12 through the control signal line 32. At
a step 212, the charge/discharge control part 28 acquires the
battery temperature Tb from the battery control part 12 through the
control signal line 32.
[0045] FIG. 4 is a graph showing function expression of a preset
charge end voltage Vc to the battery temperature Tb of the
secondary battery 11 in the case of charge at the charging current
value I1 of 160 A, 180 A and 200 A. The function expression is set
so that the state of charge at the completion of charge is 75%. The
preset charge end voltage Vc is a linear function of the battery
temperature Tb by applying the charging current value I1 as a
parameter. As the battery temperature Tb becomes higher and the
charging current value I1 becomes lower, the preset charge end
voltage Vc becomes lower. The charge/discharge control part 28
stores the function expression in FIG. 4 for each charging current
value I1.
[0046] Control accuracy of charge of the secondary battery 11 can
be improved (dischargeable capacity at the completion of charge
corresponds to a target value) by lowering the preset charge end
voltage Vc for discontinuing quick charge (by deciding the preset
charge end voltage Vc according the function expression in FIG. 4)
as the battery temperature Tb becomes higher and the charging
current value I1 becomes smaller. It can be prevented that the life
of the secondary battery 11 is shortened due to overcharge and that
a failure in the operation of the automatic guided vehicle is
caused by insufficient charge.
[0047] Returning to FIG. 2, at a step 213, the charge/discharge
control part 28 acquires the preset charge end voltage Vc from the
charging current value I1 and the battery temperature Tb (according
to the function expression in FIG. 4). It is determined whether or
not the voltage V of the secondary battery 11 equals the preset
charge end voltage Vc or more (step 214). When the voltage V of the
secondary battery 11 equals the preset charge end voltage Vc or
less, the operation returns to a step 211 and continues quick
charge. When the voltage V of the secondary battery 11 is higher
than the preset charge end voltage Vc, quick charge is finished
(step 215). The automatic guided vehicle 10 start running and
leaves the charge station. The operation returns to the step 201.
At the steps 210 to 215, charge is conducted according to the first
charge control method. As mentioned above, since the secondary
battery 11 is not charged fully in quick charge according to the
first charge control method, increase in internal pressure of the
secondary battery 11 can be prevented. Further, since the secondary
battery 11 is charged with a high current in a first charge control
method, charge can be completed in a short time (many secondary
batteries 11 for automatic guided vehicle can be maintained by a
small number of charge/discharge units).
[0048] In the case where it is determined that the discharge end
voltage Vend is smaller than the preset minimum voltage Vr at the
step 203, the operation proceeds to a step 220. The
charge/discharge control part 28 switches the charge/discharge part
25 to a discharger and discharges the battery 11 until the voltage
acquired from the battery control part 12 reaches the discharge end
voltage (full discharge) (step 220). The charge/discharge control
part 28 switches the charge/discharge part 25 to a charger,
controls a charging current value I2 received from the current
detection part 27 to be 10 A, and starts charging (step 221). The
charging current value I2 is smaller than the charging current
value I1 according to the first charge control method. Charge is
continued for a predetermined period (step 222). The predetermined
period at the step 222 is set to be a period necessary for full
charge of the secondary battery 11. Charge is finished at a step
223. The operation returns to the step 201. At the steps 220 to
223, charge is conducted according to a second charge control
method.
[0049] Since the secondary battery 11 is discharged fully at the
step 220 and charged fully according to the second charge control
method, it is possible to equalize memory effect on the secondary
battery 11 and the dispersion of voltages of respective single
cells. Since the secondary battery 11 is charged fully with a
relatively low current in the second charge control method, damage
of the secondary battery 11 due to rapid increase in its internal
pressure can be prevented.
[0050] <<Second Embodiment>>
[0051] Referring to FIG. 1 and FIG. 5, a method of controlling
charge and discharge of a secondary battery for automatic guided
vehicle in accordance with a second embodiment of the present
invention will be described. The method of controlling charge and
discharge of the secondary battery for automatic guided vehicle in
accordance with the second embodiment applies to the same system of
controlling charge and discharge of the automatic guided vehicle 10
as in the first embodiment (FIG. 1). FIG. 1 has been already
described above.
[0052] The method of controlling charge and discharge of a
secondary battery for automatic guided vehicle in accordance with a
second embodiment is different from the method of the first
embodiment only in the second charge control method. Specifically,
the steps 221 to 223 in FIG. 2 (the second charge control method)
are replaced with steps 220, 221 and 501 to 503 in FIG. 5. Only the
different steps in the second embodiment will be described
below.
[0053] FIG. 5 is a flow chart of the method of controlling charge
and discharge of a secondary battery for automatic guided vehicle
in accordance with the second embodiment. After full discharge
(step 220), the charge/discharge control part 28 switches the
charge/discharge part 25 to a charger, controls a charging current
value I2 received from the current detection part 27 to be 10 A,
and starts charging (step 221). The charging current value I2 is
smaller than the charging current value I1 according to the first
charge control method. At a step 501, the charge/discharge control
part 28 acquires the battery temperature Tb from the battery
control part 12 through the control signal line 32. At a step 502,
the charge/discharge control part 28 calculates a time variation
rate dTb/dt (t is time) and determines whether or not the rate
equals a threshold value or more. When the rate is smaller than the
threshold value, the operation returns to a step 501 and charge is
continued. When the rate equals the threshold value or more, the
operation proceeds to a step 503 and charge is finished.
[0054] The temperature Tb of the secondary battery 11 increases
with the progress of charge and the rate of increase per unit of
time rises steeply just before the completion of full charge.
Therefore, full charge can be detected by the rate of increase of
the battery temperature Tb.
[0055] According to the present invention, it is possible to obtain
an advantageous effect of realizing a method of controlling charge
and discharge of the secondary battery for automatic guided vehicle
that accurately judges the timing of refresh charge and discharge
of the secondary battery for automatic guided vehicle and minimizes
the frequency of refresh charge and discharge.
[0056] While preferred embodiments of the present invention have
been described in detail to a certain degree, it is to be
understood that, within the scope and spirit of the claims made
herein, the invention may be practiced otherwise than as
specifically described herein, the invention may be modified in
arrangement and detail without departing from such scope and
spirit.
* * * * *